For example, mineral water is made into a commercial product through various processes such as special filtration, sedimentation, heat sterilization, etc. effected on raw mater obtained from a specified water source or spring. In this regard, if a transporting vessel and/or storage vessel for the raw water or a pipeline used in bottling is/are contaminated with microorganism, chemical substance or the like or if other commercial article, a cleaning agent, or the like remains in e.g. the bottling pipeline, this can sometimes add stench or unwanted flavor to the product to be obtained.
Further, since soft drink products such as juice are also made mainly from water, such causes as above can sometimes add stench thereto.
With some types of contaminants, even such a trace amount thereof as one-millionth or less, is felt as stench. Therefore, prevention, monitoring and control against mixing of stench giving substance or flavoring agent are very important. Further, if waste water generated from a sewage plant or various industrial plants contains any stenchful or odorous substance remaining therein, this gives significant trouble and health hazard to local inhabitants. Hence, management of stenchful substance in waster water is also important.
For the above reasons, human sensory evaluation testing has been conducted as means for detecting stench or unwanted flavor. However, with food processing plants, sewage plants and various industrial plants, the atmosphere therein is often filled with odorous components. Thus, the sensory evaluation test, if conducted on site at such places, often suffers low accuracy due to the masking effect from the atmosphere therein. In addition, it may be said that the sensory evaluation test lacks objectivity, since there occurs irregularity in the evaluation result depending on the physical condition of the evaluating panelists.
On the other hand, as an evaluation testing method using machinery, a gas chromatography device, a gas chromatography/mass spectrometer, or the like are often employed. Most of these machines are highly sensitive machines capable of detecting as little as 0.1 ng of sample of each component for most kinds of compounds. However, these machines are sophisticated and expensive machines requiring special knowledge for their operations. Therefore, these machines cannot not be installed in a process in a plant or processing plate for easy operation. Moreover, as these machines require a significant amount of time and labor from preprocessing of a sample to be determined to result evaluation, they are not suitable for use for occasions or sections where the result is needed immediately.
On the other hand, as a sensor for detecting a volatile component in natural atmosphere, there are known a metal oxide semiconductor type gas sensor, a hot-wire gas sensor, a solid electrolyte type gas sensor, an infrared type gas sensor, etc. These gas sensors are compact, inexpensive and can be easily handled as well. However, as these sensors are affected by temperature variation, humidity variation of the atmosphere, unwanted gas mixed in the atmosphere, etc., such sensors alone cannot be used for detection of a trace amount of volatile organic compound contained in such atmospheres as above. Then, for instance, the metal oxide semiconductor type gas sensor capable of detecting gaseous species with the highest precision can detect a volatile component at a ppb (one-billionth) level under an atmospheric condition with exclusion of the variable factors such as temperature, humidity, mixing gas, etc.
The convention has proposed also a detecting apparatus for a volatile dissolved substance so that a volatile dissolved substance contained in liquid such as raw water can be positively evaporated for detection by means of a relatively simple sensor which is compact, low-priced and can be handled relatively easily, even when the sensor is used in a process conducted in a plant or processing plant whose atmosphere is filled with a significant amount of odorous or unwanted flavoring component. This detecting apparatus includes a sample vessel capable of holding therein an approximately fixed amount of liquid with leaving a free space at an upper inner section thereof, a nozzle capable of blowing off bubbles into the liquid held in the sample vessel, and a pressurized gas feeding device capable of feeding pressurized gas to said nozzle for the blowing of the bubbles. Within a communication passage communicating with the upper section of the sample vessel, there is exposed a detecting portion of a sensor capable of detecting a volatile component. In operation, the sensor can detect the volatile component which has evaporated from the liquid in the sample vessel and entered the communication passage. Namely, according to this conventional detecting apparatus, for enabling precision detection of the volatile component under a predetermined condition, a pre-measured, approximately fixed amount of liquid is charged into the sample vessel, so that the volatile component evaporated from this approximately fixed amount of liquid may be detected by the sensor (see e.g. Patent Document 1).
Patent Document Japanese Patent Application “Kokai” No. 11-83701